frequency generator

Electrical engineer and music enthusiast [Freidrich Trautwein] was dissatisfied. He believed that the equal tempered scale of the piano limited a player’s room for expression. And so in 1930, [Trautwein] and an accomplished pianist named [Oskar Sala] began work on an electro-mechanical instrument that would bring the glissando of the string section’s fretless fingerboards to the keyboard player. [Trautwein] called his creation the Trautonium.

Sound is produced in the instrument by sawtooth frequency generators. It is then passed through filters and manipulated by the resistive string-based manuals. Frequency and intonation are varied relative to the position of the player’s finger along a length of non-conductive string and to the amount of pressure applied. This resistive string is suspended above a conductive metal strip between a pair of posts. A small voltage is applied to the posts so that when the string touches the metal strip below, the player manipulates a voltage-controlled oscillator. A series of metal tongues, also non-conductive, hover above the string. These are placed at scale intervals and can be used like keys.

This early synthesizer is capable of producing many kinds of sounds, from crisp chirps to wet, slapping sounds and everything in between. In fact, all of the sound effects in Alfred Hitchcock’s thriller The Birds were produced on a modified Trautonium by the instrument’s one and only master, [Oskar Sala]. He went on to score hundreds of films by watching them with the Trautonium at his fingertips, recording and layering his compositions into an eerie wall of sound.

One of the acronyms you may hear thrown around is DDS which stands for Direct Digital Synthesis. DDS can be as simple as taking a digital value — a collection of ones and zeroes — and processing it through a Digital to Analog Converter (DAC) circuit. For example, if the digital source is the output of a counter that counts up to a maximum value and resets then the output of the DAC would be a ramp (analog signal) that increases in voltage until it resets back to its starting voltage.

This concept can be very useful for creating signals for use in a project or as a poor-man’s version of a signal or function generator. With this in mind I set out here to demonstrate some basic waveforms using programmable logic for flexibility, and a small collection of resistors to act as a cheap DAC. In the end I will also demonstrate an off-the-shelf and inexpensive DDS chip that can be used with any of the popular micro-controller boards available that support SPI serial communication.

All of the topics covered in the video are also discussed further after the break.

Here’s further proof that you should never leave anything of value in your hotel room. We’re not worried about someone getting in while the room is occupied. But these methods of defeating the chain lock and opening the door without a keycard (YouTube login required) do show how easy it is for the bad guys to steal your stuff.

iPhone frequency generator

Need one more way to make that iPhone a useful lab tool? Why not use it as a frequency generator. Start with a free app and mix in an audio cable with test leads and you’re in business.

Drag Soldering

[Andrei] sent us a link to a video about drag soldering. This is a method of soldering fine-pitch chips using a small bit of solder and a fat solder tip. The link he sent is dead now but we found another great example of the process. We were just using this method earlier in the week to solder a TSSOP38 package for an upcoming project and it worked like a charm.

Laser etched PCB

Here’s some art in PCB form thanks to a laser. We thought this might be interesting to share after seeing those art pieces made from old circuit boards. This example is laser etched, but not directly. As you probably guessed, the copper clad board is coated with resist and the laser etches some of it away. Whatever got zapped by the laser dissolves when the board is placed in acid, leaving [Riley Porter’s] art behind.